using System;

​

public class Program

{

    public static void Main()

    {

        //Console.WriteLine("Hello World");

        LinkList l = new LinkList();

        l.Create();

        l.Print();

        //l.Reverse();

        //l.Print();

        //l.head = l.ReverseKNodes(4, l.head);

        l.head = l.ReverseAltKNodes(l.head, 2);

        l.Print();

    }

}

​

public class Node

{

    public int data;

    public Node next;

    public Node(int d)

    {

        next = null;

        data = d;

    }

}

​

public class LinkList

{

    public Node head = null;

    public void Create()

    {

        head = new Node(2);

        Node newnode1 = new Node(3);

        head.next = newnode1;

        Node newnode2 = new Node(4);

        newnode1.next = newnode2;

        Node newnode3 = new Node(5);

        newnode2.next = newnode3;

        Node newnode4 = new Node(6);

        newnode3.next = newnode4;

        Node newnode5 = new Node(7);

        newnode4.next = newnode5;

    }

​

    public void Print()

    {

        Node temp = head;

        while (temp != null)

        {

            Console.Write(temp.next == null ? temp.data.ToString() : temp.data + "->");

            temp = temp.next;

        }

​

        Console.WriteLine();

    }

​

    public void Reverse()

    {

        Node previous = null;

        Node current = head;

        Node after = null;

        while (current != null)

        {

            after = current.next;

            current.next = previous;

            previous = current;

            current = after;

        }

​

        head = previous;

    }

​

    public Node ReverseKNodes(int k, Node head1)

    {

        int count = 0;

        Node previous = null;

        Node current = head1;

        Node after = null;

        Node temp = current;

        int check = 0;

        while (temp != null && check < k)

        {

            check++;

            temp = temp.next;

        }

​

        if (check < k)

            return current;

        while (current != null && count < k)

        {

            count++;

            after = current.next;

            current.next = previous;

            previous = current;

            current = after;

        }

​

        if (after != null)

        {

            head1.next = ReverseKNodes(k, after);

        }

​

        return previous;

    }

​

    public Node ReverseAltKNodes(Node head1, int k)

    {

        Node current = head1;

        Node previous = null;

        Node after = null;

        int c = 0;

        while (current != null && c < k)

        {

            after = current.next;

            current.next = previous;

            previous = current;

            current = after;

            c++;

        }

​

        if (head1 != null)

            head1.next = current;

        int count = 0;

        while (count < k - 1 && current != null)

        {

            current = current.next;

            count++;

        }

​

        if (current != null)

        {

            current.next = ReverseAltKNodes(current.next, k);

        }

​

        return previous;

    }

}